1. Field of the Invention
This invention is concerned with improvements in or relating to sound deadening materials and generally relates to sound deadening material of the heat fusible type in sheet or pad form or for cold application employing adhesives for bonding.
Sound deadening materials of the heat fusible type are well known and used in large quantities in automobiles, dishwashing machines and other applications where it is desired to reduce the noise arising from resonant vibrations of the sheet metal panels.
Heat fusible sound deadening material in sheet or pad form, is most often adhered to metal panels by simply laying a pad of sound deadening material on a metal panel and heating the two together. This may conveniently be applied as the panels travel along a conveyor belt towards an oven. The self adhesive properties of a sound deadening material at elevated temperatures may be utilised to create a bond of one with the other.
Alternatively, an adhesive may be applied to either or both surfaces to enable a bond to be made at room temperature. In either case the bond needs to have high tenacity in order to meet the conditions of application in the factory and subsequent to that, e.g. up to 180.degree. C. in the oven and later possible extreme cold in usage with the need to obviate the possibility of the sound deadening material breaking away with time and vibration. A requirement of such a sound deadening material is that it have excellent adhesion properties.
When a sound deadening material is applied to a surface which would be adversely affected by heating e.g. when laminated to timber for noise reduction in buildings, the method of laminating one to the other may be with adhesives applied in the usual manner. Likewise there are situations where it is simply more convenient to use adhesive bonding.
2. Discussion of the Prior Art
Well known heat fusible sound deadening materials are those based on bitumen and hence necessarily black in colour. Bituminous materials of this type are disclosed in Australian Patent Specification Nos. 34339, 405091, 498,074, 560006 and 606877. There are practical disadvantages in using such bitumen based materials which include their appearance and inferior sound deadening properties.
U.S. Pat. No. 3,424,270 and its division U.S. Pat. No. 3,652,360 are concerned with sound blocking structural elements for airborne sound. The Specifications disclose the use of a number of polymers including PVC and acrylonitrile rubbers. The combination of PVC and acrylonitrile rubbers is well known in the art and has been used since 1942. Indeed, L. A. Utrachi, Polymer Blends and Alloys, Hanser Publishers, 1989, pp 4, "The PVC/NBR blend was the first commercial thermoplastic blend in the modern sense of the word. " U.S. Pat. No. 3,424,270 and its division U.S. Pat. No. 3,652,360 also disclose the use of natural rubber and barium sulphate composition in the cured and uncured form, as part of a sound deadening laminate. However, the efficiency of the materials provided by such proposals is, to some extent, limited by the amount of filler which can be incorporated into the formulation without compromising the adhesion and flexibility of the material in sheet or pad form.
U.S. Pat. No. 4,420,341, "Stabilized Surface Modified Fillers" proposes the treatment of various fillers including calcium carbonate with various saturated and unsaturated fatty acids generally in combination with each other. The Specification requires that the fatty acid is always used in combination with an antioxidant to prevent the degradation of the "surfied filler" both during and after addition of the fatty acid to the filler. In addition the technique disclosed in U.S. Pat. No. 4,420,341 teaches that it is advantageous to promote the acid filler reaction in the shortest time possible so that exposure to air and heat are minimised. The specification teaches that with very fine fillers it can be advantageous to also purge the filler before and during surfation with an inert gas such as nitrogen to prevent or reduce exposure to air before use. Such procedures are not suited to the economical production of sound deadening materials in high volumes.
A number of prior art patents disclose the use of esters of ricinoleic acid as coupling agents applied to fillers including calcium carbonate. U.S. Pat. No. 4,704,238 uses a number of aliphatic alcohol/fatty acid esters including esters of ricinoleic acid. UK Patent Application GB 2 031 910 A, discloses the use of fatty acid esters of mono and polyhydric alcohols as coupling agents particularly for calcium carbonate and polymeric materials. Included among the fatty acids for the manufacture of such esters is ricinoleic acid. However, none of these prior specifications show the use of such techniques to produce superior sound deadening materials.
French Patent 1,489,806 discloses a process for improving reinforcing fillers for elastomers in which very fine fillers show improved dispersion following treatment with dispersing agents. Various dispersing agents are proposed. The specification teaches that the properties of reinforcing fillers are more favourable when their fineness is greater. However, the specification is specifically directed to silica and silicate fillers and does not address the suitability of such treated fillers for use in sound deadening materials. Moreover the treatment procedures exemplified are not suited to the economical production of sound deadening materials in high volumes.